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Salvatore MF. Dopamine Signaling in Substantia Nigra and Its Impact on Locomotor Function-Not a New Concept, but Neglected Reality. Int J Mol Sci 2024; 25:1131. [PMID: 38256204 PMCID: PMC10815979 DOI: 10.3390/ijms25021131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 01/11/2024] [Accepted: 01/13/2024] [Indexed: 01/24/2024] Open
Abstract
The mechanistic influences of dopamine (DA) signaling and impact on motor function are nearly always interpreted from changes in nigrostriatal neuron terminals in striatum. This is a standard practice in studies of human Parkinson's disease (PD) and aging and related animal models of PD and aging-related parkinsonism. However, despite dozens of studies indicating an ambiguous relationship between changes in striatal DA signaling and motor phenotype, this perseverating focus on striatum continues. Although DA release in substantia nigra (SN) was first reported almost 50 years ago, assessment of nigral DA signaling changes in relation to motor function is rarely considered. Whereas DA signaling has been well-characterized in striatum at all five steps of neurotransmission (biosynthesis and turnover, storage, release, reuptake, and post-synaptic binding) in the nigrostriatal pathway, the depth of such interrogations in the SN, outside of cell counts, is sparse. However, there is sufficient evidence that these steps in DA neurotransmission in the SN are operational and regulated autonomously from striatum and are present in human PD and aging and related animal models. To complete our understanding of how nigrostriatal DA signaling affects motor function, it is past time to include interrogation of nigral DA signaling. This brief review highlights evidence that changes in nigral DA signaling at each step in DA neurotransmission are autonomous from those in striatum and changes in the SN alone can influence locomotor function. Accordingly, for full characterization of how nigrostriatal DA signaling affects locomotor activity, interrogation of DA signaling in SN is essential.
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Affiliation(s)
- Michael F Salvatore
- Department of Pharmacology & Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76107, USA
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Kasanga EA, Han Y, Shifflet MK, Navarrete W, McManus R, Parry C, Barahona A, Nejtek VA, Manfredsson FP, Kordower JH, Richardson JR, Salvatore MF. Nigral-specific increase in ser31 phosphorylation compensates for tyrosine hydroxylase protein and nigrostriatal neuron loss: Implications for delaying parkinsonian signs. Exp Neurol 2023; 368:114509. [PMID: 37634696 DOI: 10.1016/j.expneurol.2023.114509] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 08/08/2023] [Accepted: 08/23/2023] [Indexed: 08/29/2023]
Abstract
Compensatory mechanisms that augment dopamine (DA) signaling are thought to mitigate onset of hypokinesia prior to major loss of tyrosine hydroxylase (TH) in striatum that occurs in Parkinson's disease. However, the identity of such mechanisms remains elusive. In the present study, the rat nigrostriatal pathway was unilaterally-lesioned with 6-hydroxydopamine (6-OHDA) to determine whether differences in DA content, TH protein, TH phosphorylation, or D1 receptor expression in striatum or substantia nigra (SN) aligned with hypokinesia onset and severity at two time points. In striatum, DA and TH loss reached its maximum (>90%) 7 days after lesion induction. However, in SN, no DA loss occurred, despite ∼60% TH loss. Hypokinesia was established at 21 days post-lesion and maintained at 28 days. At this time, DA loss was ∼60% in the SN, but still of lesser magnitude than TH loss. At day 7 and 28, ser31 TH phosphorylation increased only in SN, corresponding to less DA versus TH protein loss. In contrast, ser40 TH phosphorylation was unaffected in either region. Despite DA loss in both regions at day 28, D1 receptor expression increased only in lesioned SN. These results support the concept that augmented components of DA signaling in the SN, through increased ser31 TH phosphorylation and D1 receptor expression, contribute as compensatory mechanisms against progressive nigrostriatal neuron and TH protein loss, and may mitigate hypokinesia severity.
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Affiliation(s)
- Ella A Kasanga
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Yoonhee Han
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Marla K Shifflet
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Walter Navarrete
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Robert McManus
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Caleb Parry
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Arturo Barahona
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Vicki A Nejtek
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA
| | - Fredric P Manfredsson
- Parkinson's Disease Research Unit, Department of Translational Neuroscience, Barrow Neurological Institute, Phoenix, AZ 85013, USA
| | - Jeffrey H Kordower
- ASU-Banner Neurodegenerative Disease Research Center, Arizona State University, Tempe, AZ 85287, USA
| | - Jason R Richardson
- Robert Stempel School of Public Health and Social Work, Florida International University, Miami, FL 33199, USA
| | - Michael F Salvatore
- Department of Pharmacology and Neuroscience, University of North Texas Health Science Center, Fort Worth, TX 76117, USA.
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Statz M, Schleuter F, Weber H, Kober M, Plocksties F, Timmermann D, Storch A, Fauser M. Subthalamic nucleus deep brain stimulation does not alter growth factor expression in a rat model of stable dopaminergic deficiency. Neurosci Lett 2023; 814:137459. [PMID: 37625613 DOI: 10.1016/j.neulet.2023.137459] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 08/11/2023] [Accepted: 08/21/2023] [Indexed: 08/27/2023]
Abstract
BACKGROUND Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been a highly effective treatment option for mid-to-late-stage Parkinson's disease (PD) for decades. Besides direct effects on brain networks, neuroprotective effects of STN-DBS - potentially via alterations of growth factor expression levels - have been proposed as additional mechanisms of action. OBJECTIVE In the context of clarifying DBS mechanisms, we analyzed brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) levels in the basal ganglia, motor and parietal cortices, and dentate gyrus in an animal model of stable, severe dopaminergic deficiency. METHODS We applied one week of continuous unilateral STN-DBS in a group of stable 6-hydroxydopamine (6-OHDA) hemiparkinsonian rats (6-OHDASTIM) in comparison to a 6-OHDA control group (6-OHDASHAM) as well as healthy controls (CTRLSTIM and CTRLSHAM). BDNF and GDNF levels were determined via ELISAs. RESULTS The 6-OHDA lesion did not result in a persistent alteration in either BDNF or GDNF levels in a model of severe dopaminergic deficiency after completion of the dopaminergic degeneration. STN-DBS modestly increased BDNF levels in the entopeduncular nucleus, but even impaired BDNF and GDNF expression in cortical areas. CONCLUSIONS STN-DBS does not increase growth factor expression when applied to a model of completed, severe dopaminergic deficiency in contrast to other studies in models of modest and ongoing dopaminergic degeneration. In healthy controls, STN-DBS does not influence BDNF or GDNF expression. We consider these findings relevant for clinical purposes since DBS in PD is usually applied late in the course of the disease.
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Affiliation(s)
- Meike Statz
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany
| | - Frederike Schleuter
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany
| | - Hanna Weber
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany
| | - Maria Kober
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany
| | - Franz Plocksties
- Institute of Applied Microelectronics and Computer Engineering, University of Rostock, Albert-Einstein-Str. 26, 18119 Rostock, Germany
| | - Dirk Timmermann
- Institute of Applied Microelectronics and Computer Engineering, University of Rostock, Albert-Einstein-Str. 26, 18119 Rostock, Germany
| | - Alexander Storch
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany; German Centre for Neurodegenerative Diseases (DZNE) Rostock/Greifswald, Gehlsheimer Str. 20, 18147 Rostock, Germany
| | - Mareike Fauser
- Department of Neurology, University of Rostock, Gehlsheimer Str. 20, 18147 Rostock, Germany.
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